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                <ol class="chapter"><li class="chapter-item expanded "><a href="../ch01-00-get-excited.html"><strong aria-hidden="true">1.</strong> Get excited</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../index.html"><strong aria-hidden="true">1.1.</strong> Check out the README</a></li><li class="chapter-item expanded "><a href="../Demo.html"><strong aria-hidden="true">1.2.</strong> See the demo</a></li></ol></li><li class="chapter-item expanded "><a href="../ch02-00-learn-to-use.html"><strong aria-hidden="true">2.</strong> Learn to use Watermelon</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../Installation.html"><strong aria-hidden="true">2.1.</strong> Installation</a></li><li class="chapter-item expanded "><a href="../Setup.html"><strong aria-hidden="true">2.2.</strong> Setup</a></li><li class="chapter-item expanded "><a href="../Schema.html"><strong aria-hidden="true">2.3.</strong> Schema</a></li><li class="chapter-item expanded "><a href="../Model.html"><strong aria-hidden="true">2.4.</strong> Defining Models</a></li><li class="chapter-item expanded "><a href="../CRUD.html"><strong aria-hidden="true">2.5.</strong> Create, Read, Update, Delete</a></li><li class="chapter-item expanded "><a href="../Components.html"><strong aria-hidden="true">2.6.</strong> Connecting to React Components</a></li><li class="chapter-item expanded "><a href="../Query.html"><strong aria-hidden="true">2.7.</strong> Querying</a></li><li class="chapter-item expanded "><a href="../Relation.html"><strong aria-hidden="true">2.8.</strong> Relations</a></li><li class="chapter-item expanded "><a href="../Actions.html"><strong aria-hidden="true">2.9.</strong> Custom Actions</a></li></ol></li><li class="chapter-item expanded "><a href="../ch03-00-advanced.html"><strong aria-hidden="true">3.</strong> Advanced guides</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../Advanced/Migrations.html"><strong aria-hidden="true">3.1.</strong> Migrations</a></li><li class="chapter-item expanded "><a href="../Advanced/Sync.html"><strong aria-hidden="true">3.2.</strong> Sync</a></li><li class="chapter-item expanded "><a href="../Advanced/CreateUpdateTracking.html"><strong aria-hidden="true">3.3.</strong> Automatic create/update tracking</a></li><li class="chapter-item expanded "><a href="../Advanced/AdvancedFields.html"><strong aria-hidden="true">3.4.</strong> Advanced fields</a></li><li class="chapter-item expanded "><a href="../Advanced/Flow.html" class="active"><strong aria-hidden="true">3.5.</strong> Flow</a></li><li class="chapter-item expanded "><a href="../Advanced/LocalStorage.html"><strong aria-hidden="true">3.6.</strong> LocalStorage</a></li><li class="chapter-item expanded "><a href="../Advanced/ProTips.html"><strong aria-hidden="true">3.7.</strong> Pro tips</a></li><li class="chapter-item expanded "><a href="../Advanced/Performance.html"><strong aria-hidden="true">3.8.</strong> Performance tips</a></li><li class="chapter-item expanded "><a href="../Advanced/SharingDatabaseAcrossTargets.html"><strong aria-hidden="true">3.9.</strong> iOS - Sharing database across targets</a></li></ol></li><li class="chapter-item expanded "><a href="../ch04-00-deeper.html"><strong aria-hidden="true">4.</strong> Dig deeper into WatermelonDB</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../Implementation/Architecture.html"><strong aria-hidden="true">4.1.</strong> Architecture</a></li><li class="chapter-item expanded "><a href="../Implementation/Adapters.html"><strong aria-hidden="true">4.2.</strong> Adapters</a></li><li class="chapter-item expanded "><a href="../Implementation/SyncImpl.html"><strong aria-hidden="true">4.3.</strong> Sync implementation</a></li></ol></li><li class="chapter-item expanded "><a href="../ch04-00-deeper.html"><strong aria-hidden="true">5.</strong> Other</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../Roadmap.html"><strong aria-hidden="true">5.1.</strong> Roadmap</a></li><li class="chapter-item expanded "><a href="../CONTRIBUTING.html"><strong aria-hidden="true">5.2.</strong> Contributing</a></li><li class="chapter-item expanded "><a href="../CHANGELOG.html"><strong aria-hidden="true">5.3.</strong> Changelog</a></li></ol></li></ol>
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                        <h1 id="watermelon--flow"><a class="header" href="#watermelon--flow">Watermelon ❤️ Flow</a></h1>
<p>Watermelon was developed with <a href="https://flow.org">Flow</a> in mind.</p>
<p>If you're a Flow user yourself (and we highly recommend it!), here's some things you need to keep in mind:</p>
<h2 id="setup"><a class="header" href="#setup">Setup</a></h2>
<p>Add this to your <code>.flowconfig</code> file so that Flow can see Watermelon's types.</p>
<pre><code class="language-ini">[options]

module.name_mapper='^@nozbe/watermelondb\(.*\)$' -&gt; '&lt;PROJECT_ROOT&gt;/node_modules/@nozbe/watermelondb/src\1'
</code></pre>
<p>Note that this won't work if you put the entire <code>node_modules/</code> folder under the <code>[ignore]</code> section. In that case, change it to only ignore the specific node modules that throw errors in your app, so that Flow can scan Watermelon files.</p>
<h2 id="tables-and-columns"><a class="header" href="#tables-and-columns">Tables and columns</a></h2>
<p>Table and column names are <strong>opaque types</strong> in Flow.</p>
<p>So if you try to use simple strings, like so:</p>
<pre><code class="language-js">class Comment extends Model {
  static table = 'comments'

  @text('body') body
}
</code></pre>
<p>You'll get errors, because you're passing <code>'comments'</code> (a <code>string</code>) where <code>TableName&lt;Comment&gt;</code> is expected, and <code>'body'</code> (again, a <code>string</code>) where <code>ColumnName</code> is expected.</p>
<p>When using Watermelon with Flow, you must pre-define all your table and column names in one place, then only use those symbols (and not strings) in all other places.</p>
<p>We recommend defining symbols like this:</p>
<pre><code class="language-js">// File: model/schema.js
// @flow

import { tableName, columnName, type TableName, appSchema, tableSchema } from '@nozbe/watermelondb'
import type Comment from './Comment.js'

export const Tables = {
  comments: (tableName('comments'): TableName&lt;Comment&gt;),
  // ...
}

export const Columns = {
  comments: {
    body: columnName('body'),
    // ...
  }
}

export const appSchema = appSchema({
  version: 1,
  tables: [
    tableSchema({
      name: Tables.comments,
      columns: [
        { name: Columns.comments.body, type: 'string' },
      ],
    }),
    // ...
  ]
})
</code></pre>
<p>And then using them like so:</p>
<pre><code class="language-js">// File: model/Comment.js
// @flow

import { Model } from '@nozbe/watermelondb'
import { text } from '@nozbe/watermelondb/decorators'

import { Tables, Columns } from './schema.js'

const Column = Columns.comments

export default class Comment extends Model {
  static table = Tables.comments

  @text(Column.body) body: string
}
</code></pre>
<h3 id="but-isnt-that-a-lot-of-boilerplate"><a class="header" href="#but-isnt-that-a-lot-of-boilerplate">But isn't that a lot of boilerplate?</a></h3>
<p>Yes, it looks more boilerplate'y than the non-Flow examples, however:</p>
<ul>
<li>you're protected from typos — strings are defined once</li>
<li>easier refactoring — you only change column name in one place</li>
<li>no orphan columns or tables — no way to accidentally refer to a column or table that was removed from the schema</li>
<li><code>TableName</code> is typed with the model class it refers to, which allows Flow to find other mistakes in your code</li>
</ul>
<p>In general, we find that untyped string constants lead to bugs, and defining typed constants is a good practice.</p>
<h3 id="associations"><a class="header" href="#associations">associations</a></h3>
<p>When using Flow, you define model associations like this:</p>
<pre><code class="language-js">import { Model, associations } from '@nozbe/watermelondb'
import { Tables, Columns } from './schema.js'

const Column = Columns.posts

class Post extends Model {
  static table = Tables.posts
  static associations = associations(
    [Tables.comments, { type: 'has_many', foreignKey: Columns.comments.postId }],
    [Tables.users, { type: 'belongs_to', key: Column.authorId }],
  )
}
</code></pre>
<h2 id="common-types"><a class="header" href="#common-types">Common types</a></h2>
<p>Many types are tagged with the model class the type refers to:</p>
<pre><code class="language-js">TableName&lt;Post&gt; // a table name referring to posts
Collection&lt;Post&gt; // the Collection for posts
Relation&lt;Comment&gt; // a relation that can fetch a Comment
Relation&lt;?Comment&gt; // a relation that can fetch a Comment or `null`
Query&lt;Comment&gt; // a query that can fetch many Comments
</code></pre>
<p>Always mark the type of model fields. Remember to include <code>?</code> if the underlying table column is optional. Flow can't check if model fields match the schema or if they match the decorator's signature.</p>
<pre><code class="language-js">@text(Column.body) body: string
@date(Column.createdAt) createdAt: Date
@date(Column.archivedAt) archivedAt: ?Date
</code></pre>
<p>If you need to refer to an ID of a record, always use the <code>RecordId</code> type alias, not <code>string</code> (they're the same, but the former is self-documenting).</p>
<p>If you ever access the record's raw data (DON'T do that unless you <em>really</em> know what you're doing), use <code>DirtyRaw</code> to refer to raw data from external sources (database, server), and <code>RawRecord</code> after it was passed through <code>sanitizedRaw</code>.</p>

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